What is the difference between contrast and noncontrast ct scan

Contrast agents can be further classified as high or low osmolality, based on the iodine concentration. Most centers use nonionic contrast agents which are generally low osmolality for IV contrast studies. Children have a lower incidence of reactions to IV contrast agents, and most of these are mild 0.

Risk factors for contrast reactions include multiple drug allergies and asthma. Although many radiology departments screen for shellfish allergy, there is no cross-reactivity between shellfish and iodinated contrast. However, patients with a documented anaphylactic reaction to any medication are at higher risk of a reaction to iodinated contrast. Many centers screen outpatients with suspected renal insufficiency by measuring serum creatinine one month before administration of contrast agents.

Creatinine cutoffs vary among institutions, but generally range between 1. In patients with normal renal function, repeat measurement of serum creatinine is not recommended after outpatient administration of IV contrast agents.

Use of low-osmolality contrast has been associated with a reduction in adverse effects. Intrathecal iodinated contrast is given during myelography to evaluate spinal or basal cisternal disease and cerebrospinal fluid leaks. CT may also be ordered for cross-sectional images of the spine with contrast in the thecal sac. Concerns for using IV contrast during CT include a history of reactions to contrast agents, pregnancy, treatment of thyroid disease with radioactive iodine, use of metformin Glucophage , and chronic or acutely worsening renal disease.

Contrast may also be avoided when the suspected pathology is likely to be visible on noncontrast-enhanced CT. A history should be obtained to determine if the reaction was mild which typically requires observation but not treatment , moderate which requires prompt treatment , or severe which requires rapid intervention and, often, hospitalization. Possible reactions are listed in Table 1. A history of anaphylactic reactions would preclude IV contrast except in extreme emergencies.

Nausea, vomiting. Nasal stuffiness. Altered taste. Rash, hives. Swelling of eyes or face. Mild hypotension. Tachycardia or bradycardia. Bronchospasm, wheezing. Laryngeal edema. Generalized or diffuse erythema. Cardiopulmonary arrest. Clinically manifest arrhythmias.

Profound hypotension. Laryngeal edema severe or rapidly progressing. Adapted with permission from American College of Radiology. ACR manual on contrast media: version 8, November 21, Methylprednisolone Medrol , 32 mg orally 12 and 2 hours before contrast administration; plus diphenhydramine Benadryl , 50 mg intravenously, intramuscularly, or orally 1 hour before contrast administration.

Prednisone, 50 mg orally 13, 7, and 1 hour before contrast administration; plus diphenhydramine, 50 mg intravenously, intramuscularly, or orally 1 hour before contrast administration. Information from reference 7. Iodinated contrast crosses the human placenta. No mutagenic or teratogenic effects have been shown with nonionic, low-osmolality contrast in animal studies. The American College of Radiology recommends using IV iodinated contrast in pregnant women when the information needed affects the care of the patient and fetus and cannot be obtained without contrast, and when the referring physician thinks that imaging should not wait until after the pregnancy.

Iodinated contrast media can saturate the thyroid gland and significantly reduce uptake of iodine , rendering the treatment ineffective. Iodinated contrast should be avoided for two months before administration of iodine However, if contrast must be administered within two months of iodine treatment, consultation with an endocrinologist should be considered.

The risk of developing metabolic acidosis with metformin use is rare, but is higher in persons with chronic renal disease or transient impairment of renal function. There is no direct interaction between metformin and IV radiologic contrast agents. However, IV radiologic contrast may cause transient alteration in renal function, which could impair metformin clearance, leading to a higher risk of metabolic acidosis.

The U. Food and Drug Administration advises that metformin should be withheld at the time of IV contrast administration and for 48 hours afterward, and resumed only after reevaluation of renal status i. Lactic acidosis has never been documented in patients with normal renal function who are receiving metformin.

The American College of Radiology proposes a three-tiered risk assessment for patients receiving metformin in whom IV contrast is to be administered Table 3. Metformin Glucophage can be continued when contrast is administered; serum creatinine does not need to be measured. Metformin should be discontinued when contrast is administered; if the patient remains clinically stable and has no new intercurrent risk factors for renal impairment, metformin may be resumed in 48 hours without repeating serum creatinine measurement.

Metformin should be discontinued when contrast is administered; resume only after careful reevaluation and monitoring of renal status. Iodinated contrast agents can cause reversible acute renal failure. Risk factors include chronic kidney disease, diabetes mellitus, heart failure, older age, anemia, left ventricular systolic dysfunction, and contrast volume. Recent studies suggest that a combination of hydration, sodium bicarbonate, N -acetylcysteine, and decreased contrast volume may reduce this risk in high-risk populations.

The question of whether this risk has been overstated has been raised in the medical literature. One study showed similar increases in serum creatinine levels between inpatient populations who received IV iodinated contrast and those who did not.

Noncontrast-enhanced CT is used in patients with head trauma and acute stroke. Unenhanced CT is also used in patients with spine and extremity trauma. High-resolution CT, which is used to evaluate diffuse lung disease, does not use IV contrast. Noncontrast-enhanced CT of the head is the preferred initial study if performed within three hours of acute symptom onset; contrast-enhanced CT should be obtained for patients with symptoms lasting longer than three hours; contrast-enhanced CT combined with CT angiography of the neck may be needed for follow-up.

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NOPR Registry. FAQs for Participants. Imaging Information For Physicians. Cases of the Month. A CT angiogram of the chest to evaluate for aortic dissection will have the timing set so the contrast is present in the aorta. Meanwhile, a general CT of the chest with IV contrast will have the contrast timed so that it is present within the capillary bed of the soft tissues.

For the abdomen and pelvis, contrast timing is more complicated, because there are both systemic and portal venous capillary beds. Most CT scans of the abdomen and pelvis are timed so that the contrast is in the portal veins. CT scans of the brain: when is IV contrast used? IV contrast is used in brain CT when performing a CT angiogram or venogram or for evaluating an abscess or malignancy. When is IV contrast used for abdomen and pelvis CT?

There are several times when IV contrast is not necessary. These are when evaluating for ureteral calculi or retroperitoneal hematoma. For all other purposes IV contrast is strongly desirable including evaluating for infection associated with kidney stones. If a patient has a contraindication to IV contrast, the study can be performed without it. Full policy details on when oral contrast is used for CT in the ED. Generally, there is a minute delay after finishing PO contrast before performing the CT study.

When would I need rectal contrast?